A related cross drive transmission and controls therefor are shown in U.S. Pat. No. 3,611,838 Robert C. Utter, granted Oct. 12, 1971. A related hydromechanical transmission is shown in U.S. Pat. No. 3,982,448 James C. Polak and Phillip J. Ross, granted Sept. 28, 1976. Related hydrostatic transmissions and units thereof are shown in U.S. Pat. Nos. 3,274,946 Edw. E. Simmons, granted Sept. 27, 1966 and 3,752,010 R. G. Tipping, granted Aug. 14, 1973. The type of modulator valve used is shown in U.S. Pat. No. 3,093,010 W. M. Spreitzer et al., granted June 11, 1963. Speed governors, as shown in U.S. Pat. No. 2,762,384 Rosenberger, granted Sept. 11, 1956, are used. A related ratio governor is shown in U.S. Pat. No. 3,583,154 Robt. C. Utter, granted June 8, 1971. Manual electric controls are shown in U.S. Pat. No. 3,640,157 Robt. H. Schaefer, granted Feb. 8, 1972. A related zero stroke bias valve is shown in U.S. Pat. No. 3,590,577 Robt. C. Utter, granted July 6, 1971.